The present invention relates to a hydrodynamic brake which reduces the circulation of air in the space in the brake.
In the use of hydrodynamic brakes, such as retarders in vehicles, a certain brake action always arises during the propulsion of the vehicle as a consequence of the rotation of the rotor with a driving shaft of the vehicle. This brake action is caused by the air in the toroid-shaped space being forced to circulate. The circulating air provides a brake action in a way corresponding to the action of the introducable medium when the air circulates in the toroid-shaped space. The supplied medium is usually an oil having suitable properties. Although the density of the air is only a fraction of the density of the oil, the brake action arising hereby is not entirely negligible. The fuel consumption of a vehicle having a retarder therefore becomes unnecessarily high.
In order to reduce this circulation of air in the toroid-shaped space between the stator and the rotor, a plurality of different solutions have been proposed. A so-called dazzling-screen is for example used which is intended to be moved into the gap between the stator and the rotor for preventing said circulation of air, when no brake action is desired. The use of dazzling-screens includes a plurality of movable mechanical parts, which results in a complicated construction.
EP 233 331 discloses supplying a blocking medium to the toroid-shaped space of a retarder in order to reduce the circulation of air and thus to reduce the brake action obtained by the circulating air. The blocking medium is supplied radially directed in the toroid-shaped space. It is intended that the supplied blocking medium form a blocking medium curtain in the area between the stator and the rotor such that the circulation of air between the stator and the rotor is reduced. If the medium is not inserted with a sufficiently high velocity, the heavy circulation of air, which may amount to 100 m/s in the toroid-shaped space, will relatively quicky move the supplied blocking medium towards the walls of the toroid-shaped space.